Some intravascular interventional procedures produce an artificial embolism in mammals that is useful in controlling internal bleeding, blocking the blood supply to tumors, or relieving pressure in a vessel wall near an aneurysm. Known methods for producing an artificial embolism include use of (1) inflatable and detachable balloons, (2) coagulating substances, (3) later-curing polymeric substances, (4) occlusive wire coils, (5) embolization particles, and (5) supplemental occlusive embolic materials. Disadvantages relating to the known methods include recanalization, perforation of blood vessels, inadvertent downstream embolization due to fragmentation or release of trapped particles, poor positioning control, instability, imprecise sizing, and shrinkage or movement of the embolic material.
Early embolization particles were made by chopping or grinding polyvinyl alcohol (PVA) foam or sponge. Such PVA foam or sponge embolization particles are irregularly shaped and generally contain a range of pore sizes that are produced during the manufacturing process by whipping air into the PVA solution prior to crosslinking. Disadvantages of these particles include their non-precise size (aspect ratios) and open edges on the particles that cause them to clump together and subsequently plug up delivery catheters.
Spherical particles minimize these disadvantages. In addition, spherical particles can penetrate deeper into the vasculature than traditional particles due to the uniform shape of the particle. Existing spherical embolics include Biocompatibles International plc's Bead Block™ Biosphere Medical, Inc.'s Embosphere™ and Boston Scientific Corporation's Contour SE™. The Bead Block™ product is a PVA gel and does not have macropores (that is, the pores are less than 1 micron in diameter). Embosphere™ is a gel made of an acrylic co-polymer (trisacryl) and does not have macropores. Contour SE™ is made of PVA has an onion shape but has no surface macropores.
However, spherical embolization particles have several disadvantages. For example, the smooth surface of these particles may affect the stable integration of such particles within the occlusive mass comprising the particles, clotted blood and ultimately fibrous tissue. In addition, the compression of such particles is only about 20-35% in one dimension thereby limiting the size of the embolization particle that can be used in a given catheter.